Method and apparatus for injecting liquid fuel into a shaft furnace

ABSTRACT

A method for the injection of a liquid fuel into a shaft furnace, in which a jet of fuel is introduced into a chamber where it is atomized by a jet of compressed gas. The mixture of fuel and gas is then passed through at least one further chamber in which a further jet of compressed gas completes the atomization of the fuel. The mixture is then caused to converge and then diverge before being subjected to the action of a hot oxidizing gaseous fluid, whereby the fuel is burned before being injected into the furnace.

United States Patent [72] Inventor Raymond George Limpach Esch surAlzette, Grand-Duchy, Luxembourg [21] Appl. No. 802,117

[22] Filed Feb. 25,1969

[45] Patented June I, 1971 [73] Assignee Centre National De RecherchesMetallurgigues Brussels, Belgium [32] Priority Feb. 28, 1968 [33]Luxembourg [54] METHOD AND APPARATUS FOR INJECTING LIQUID FUEL INTO ASHAFT FURNACE [50] Field of Search 263/29, 30; 266/29 [56] ReferencesCited UNITED STATES PATENTS 3,383,099 5/1968 Rehder 263/29 PrimaryExaminer-John J. Camby Attorney-Holman & Stern ABSTRACT: A method forthe injection of a liquid fuel into a shaft furnace, in which a jet offuel is introduced into a chamber where it is atomized by a jet ofcompressed gas. The mixture of fuel and gas is then passed through atleast one further chamber in which a further jet of compressed gascompletes the atomization of the fuel. The mixture is then caused toconverge and then diverge before being subjected to the action of a hotoxidizing gaseous fluid, whereby the fuel is burned before beinginjected into the furnace.

N/I, I

14 Claims, 2 Drawing Figs. [52] U.S.Cl 263/29, 266/29 [5]] lnt.Cl F27b1/10 METHOD AND APPARATUS FOR INJECTING LlQUlD FUEL lNTO A SHAFT FURNACEThe invention relates to a method and apparatus for the injection ofliquid fuel into a shaft furnace.

it is well known that by injecting liquid fuel into a shaft furnace, inparticular into a blast furnace, it is possible, in good utilizationconditions, to decrease the coke rate to a substantial extent and toexercise some control over the running of the blast furnace. In spite ofthis, however, with the fuel injectors customarily used in blast furnaceoperation, frequently one does no more than ensure the introduction of amore or less compact jet of fuel oil into the current of hot air, thedispersion and atomization of the jet of fuel in the current of air notbeing in general very extensive.

Moreover, the amount of fuel which can actually be used by this methodis, relatively speaking, low. In actual fact, beyond a certain rate offlow which is rapidly reached, the jet of fuel is scarcely dispersed atall and the fuel no longer burns before leaving the combustion zone ofthe blast furnace; in addition the degree of atomization of the fuel isdependent on the rate of flow of the hot air.

In order to be able to draw the maximum benefit from the injection,while overcoming the above-mentioned disadvantages, it has already beenproposed to preheat the fuel and even to start its combustion a shorttime before it enters the furnace. lt has also already been suggestedthat the fuel should be atomiaed and mixed with an oxidizing gas, forthe purpose of facilitating the combustion of the one by the other. Someof these methods have, however, still retained certain disadvantages, inparticular the appearance of cracking under conditions which would leadto a blocking up of the injectors. Certain other of these methods wouldrequire high pressure devices for obtaining satisfactory atomization ofthe fuel. Others, which while permitting partial combustion of the fuelbefore its entry into the furnace, would require a comparative ly longdwell time of the oxidizing gas and the fuel in the injection nozzle.The same applicant, in a previous patent specification has alreadydescribed a method adapted to overcome the majority of thesedisadvantages in a highly satisfactory way. v

According to the invention, there is provided a method for the injectionof fuel into a shaft furnace, the method comprising the steps ofintroducing a jet of liquid fuel into a chamber, in which the pressureon the liquid is reduced, injecting into the chamber a jet of compressedgas which atomizes the fuel and mixes with it, passing the mixturethrough one or more secondary chambers in series with the first chamberin each of which it is subjected to the action of one or more jets ofcompressed gas, which jets enhance the atomization of the fuel,directing the mixture of fuel and gas through a convergent/divergentdevice, and subjecting the mixture at the outlet of the said device tothe action of a hot oxidizing gaseous fluid in a proportion such thatsubstantially all the fuel present in the mixture is burned before beingintroduced with the fluid into the shaft furnace.

This method ensures a high calorific combustion yield and increases theworking life of the device in which the combustion starts up anddevelops. Moreover, .the degree of atomization of the fuel andaccordingly the homogeneity of the fuel/compressed gas mixture areparticularly high.

in accordance with an advantageous variation of the method of theinvention, the jets of compressed gas are preheated before entering themixing chambers, which enables the gasification of the fuel to bestarted, this preheating being carried out preferably by means of thehot oxidizing gaseous fluid which is preferably hot air.

in accordance with another advantageous variation of this method, theoxygen content of the jets of compressed gas is higher the nearer thechamber into which they are directed is to the convergent/divergentdevice, in front of it, the jet of compressed gas in the chamberimmediately preceding the convergent/divergent device beingsubstantially richer in oxygen than the jets in the other chambers.

in this latter variation the combustion of the fuel cannot give upintense heat in the first mixing chambers, with the result that any riskof the destruction of these chambers by abnormal increase in temperatureis ruled out; combustion develops mainly in the last chamber, which isless likely to be destroyed since the gases produced by the combustionescape immediately from the chamber, and in practice there is scarcelytime for them to raise the temperature of the walls of the said lastchamber.

The invention also provides an injector by which it is possible to putthe above-described method into operation; such an apparatus is showndiagrammatically in the accompanying drawings.

ln the drawings:

FIG. It shows an injector for liquid fuel; and

FIG. 2 shows a detail of the injector illustrating an alternativeembodiment of the injector.

In the drawings, which have been given by way of example only and arenot to scale, the section of a circular air main of a blast furnace isshown at l. A branch 3, of this main is attached by a tuyere 17 to thewall 2 of a blast furnace and it is accordingly possible for hot air tobe blown into the furnace through the orifice 18.

The horizontal portion 4 of the branch surrounds a fuel injector whichis constructed as follows; a fuel line 5 opens out through orifices 7into an expansion chamber 6, where the fuel is atomized by means of jetsof compressed gas. The mixture of fuel and gas is conveyed from theexpansion chamber 6 to a secondary chamber 8, where it is againsubjected to the action of jets of compressed gas. These gases aresupplied via the conduit 10 fed at 11, and penetrate into the chambersthrough the orifices l2 and 13; an orifice 9 gives communication betweenthe chambers 6 and 8; the secondary chamber 8 opens out into aconvergent/divergent device 14/ 15, arranged to face the orifice l8formed in the wall of the furnace. A convergent nozzle 16, which isaxially displaceable, enables the length of the flame to be regulated.

In an alternative embodiment of injector, as indicated in FIG. 2, twosecondary chambers 8,21 are in series with the chamber 6 and communicatewith each other through an orifice 22. The mixture of fuel andcompressed gas passes from the chamber 8 through the orifice 22 and isagain subjected to the action of jets of compressed gas from orifices13. The mixture is further subjected to the action of an oxygen-rich gasinjected through orifices 20 opening out from a gasline 19. Partialcombustion of the fuel occurs in the chamber 21 and the mixture emergesthrough the convergent/divergent device 14.

The injector forming the subject of the invention has the essentialfeatures that it comprises:

a. A line intended to supply liquid fuel to a first chamber through atleast one orifice; I b. One or more secondary chambers in seriescommunicating with the first chamber through an orifice, and thesecondary chambers communicating successively with each other by one ormore orifices in such a way that the fuel penetrating into the firstchamber through the fuel line passes successively through the firstchamber then the secondary chamber or chambers;

c. A channel opening out, preferably tangentially, into the chambersthrough suitable inlets. This channel is intended to supply a compressedgas to the chambers, the orifices being orientated in such a way thatthe jets of compressed gas meet and atomize the jet or jets of fuelintroduced into the first chamber and that the jets of gas meet in eachsecondary chamber the fuel/compressed gas mixture issuing from the priorchamber.

d. A convergent/divergent device obturating the last secondary chamberin such a manner that the fuel and compressed gas mixture cannot leavethis chamber except by passing through the convergent/divergent device.

e. A channel intended to supply hot, oxidizing gaseous fluid to thefurnace. This channel is connected to the furnace, for instance, bymeans of a tuyere, and the convergent/divergent device sealingly opensout into the interior of the channel.

ln accordance with an advantageous modification of the injector of theinvention, the last chamber, i.e. that immediately in front of theconvergent/divergent device, has means for supplying a gas rich inoxygen, which means may open out into the last chamber through, forinstance, inlets as used for the compressed gas or through separate typeinlets.

Again in accordance with a modification of the invention, afrustoconical nozzle is arranged convergently at the oJtlet of theconvergent-divergent device so as to leave a free space between theconvergent/divergent device and the nozzle, the nozzle beingdisplaceable substantially along the axis of the injector, this havingthe advantage of making it possible to regulate the length of the flameissuing from the injector.

ln accordance with a still more advantageous modification of theinjector of the invention, the fuel line is arranged in the interior ofthe compressed gas channel which is itself disposed in the interior ofthe channel for the hot, oxidizing gaseous fluid.

The injector illustrated in the accompanying drawing enables thecompressed gas to be preheated by the hot, oxidizing gaseous fluid,while protecting the fuel from any possible cracking effect resultingfrom premature heating. Moreover, the compressed gas cools the internalwall of the channel and accordingly protects it from the heat of thefluid.

The data given below are examples only to facilitate comprehension ofthe particularly interesting advantages of the injector forming thesubject of the invention. A liquid fuel injector was constructed inaccordance with the above description with an injection capacity in anindustrial furnace of 300 kg./hr. of extra heavy fuel, heated to 100 C.;this injector functioned at a fuel pressure of 9 kg./cm. at entry; thecompressed gas used for atomizing and gasifying the fuel was injected at6 kg./cm.*, at a rate of flow of 30 nm /hr., and the hot air supplied tothe tuyere of the blast furnace was at a pressure between 1 kg./crri. to1.2 kg./cm.

The injector described was subjected to a laboratory test by which itwas possible to check its functioning characteristics. During the courseof this test, the injector was placed in a tubular electric furnace,heated to 900 C., to simulate the thermal conditions existing in theinterior of a blast furnace tuyere. Compressed air was circulated in anenvelope protecting the injector externally, and the air became heated,while still protecting the injector. Once the air came into contact withthe fuel oil in the mixing chamber it started not only a fine dispersionof the fuel oil but also the heating and gasification of the latter,with the result that at the outlet of the injector the fuel had the formnot only of a shower of fine droplets but also the form of a thick mistof gasified fuel oil; this mixture ignited spontaneously on contact witha flame, or even with a red hot bar of steel. The combustion flame ofthe fuel oil remained quite stable, even in the absence of a flame or ofa hot ignition point. The combustion flame had an elongated shape, whichwas advantageous for using this injector in the blast furnace. The flamemoreover was brilliant and its aspect indicated that good combustion wastaking place.

After the preliminary test, the injector was introduced into a blastfurnace tuyere, and its performance was compared to that of the standardinjectors with which the other tuyeres of the same furnace wereequipped. At these tuyeres, equipped with standard injectors, it was notpossible to observe any combustion flame. The fuel was in actual factliquid all the time, and unignited when it passed into the combustionzone in the interior of the furnace. On the other hand, at the tuyereequipped with the new injector, it was possible to observe a fuelcombustion flame already in the interior of the tuyere, i.e. before thecombustion zone of the coke in the furnace. It was possible to raise therate of fuel oil supplied to this new injector to a value 30 percenthigher than with standard injectors.

The rapid combustion of the liquid fuel achieved thanks to the injectordescribed above, enables larger amounts of liquid fuel to be usefullyinjected without the combustion of the fuel being affected by the normalvariations in the running of the furnace, e.g. by normal variations inthe rate of flow of hot air to the individual tuyeres.

This result constitutes a particularly important advantage of the methodof the invention, and in actual fact plays a part in reducing the cokerate to a substantial extent.

lclaim:

1. In a method for injecting fuel into a shaft furnace, comprisingintroducing a jet of liquid fuel into a first chamber, atomizing thefuel by means of a jet of compressed gas wherein the gas mixes with theatomized fuel, causing the mixture to converge and then diverge, thensubjecting the mixture to the action of a hot oxidizing gaseous fluid,and introducing the mixture of fuel gas and oxidizing fluid into theshaft furnace: the improvement comprising the steps of passing mixtureof fuel and compressed gas from said first chamber immediately throughat least one secondary chamber; introducing at least one further jet ofcompressed gas into said secon dary chamber to augment the atomizationof the fuel; and after causing the mixture to converge and then diverge,introducing the hot oxidizing gaseous fluid into the mixture in such aproportion that substantially all the fuel present in said mixture offuel and compressed gas is burned before being introduced along withsaid oxidizing fluid into the furnace.

2. The method as claimed in claim 1, comprising the further step ofpreheating at least one of said jets of compressed gas before beingintroduced into a chamber.

3. The method as claimed in claim 2, in which said preheating isperformed by said hot oxidizing gaseous fluid.

4. The method as claimed in claim 1, in which the jet of compressed gasintroduced into the last chamber through which the fuel and compressedgas mixture passes is substantially richer in oxygen than the jet ofcompressed gas in the prior chamber.

5. ln an injector for the injection of liquid fuel into a shaft furnace,comprising a first chamber, a fuel line for supplying liquid fuel tosaid first chamber through at least one orifice, at least one inlet intosaid first chamber, a channel for injecting a compressed gas into saidfirst chamber through said inlet, a convergent/divergent means throughwhich the liquid fuel and compressed gas pass, and a channel forsupplying a hot oxidizing gaseous fluid to the furnace, theconvergent/divergent means sealingly opening out into the interior ofsaid channel for hot oxidizing gaseous fluid: the improvement being atleast one secondary chamber having an orifice, the secondary chambercommunicating with said first chamber through the orifice; at least oneinjection inlet through which said channel for the compressed gas opensinto said secondary chamber; said inlet in said first chamber beingorientated such that the compressed gas injected therein mixes with andatomizes the fuel supplied into said first chamber; said inlet in saidsecondary chamber being orientated such that the compressed gas meetsthe fuel and compressed gas mixture issuing from said first chamber andaugments the atomization of the fuel; said convergent/divergent meansbeing positioned adjacent said secondary chamber so that the fuel andcompressed gas mixture can only leave said secondary chamber by passingthrough the said means.

6. The injector as claimed in claim 5, further comprising afrustoconical nozzle arranged convergently at the outlet of saidconvergent/divergent means so as to leave a space between said means andthe nozzle, said nozzle being displaceable substantially along the axisof the injector.

7. The injector as claimed in claim 5, further comprising means forsupplying a gas rich in oxygen to the secondary chamber immediatelybefore said convergent/divergent means.

8. The injector as claimed in claim 5, wherein said fuel line isarranged in the interior of said compressed gas channel, which channelis arranged in the interior of said channel for the hot oxidizinggaseous fluid.

9. In an injector for the injection of liquid fuel into a shaft furnace,comprising a first chamber, a fuel line for supplying liquid fuel tosaid first chamber through at least one orifice, at least one inlet intosaid first chamber, a channel for injecting a compressed gas into saidfirst chamber through the said at least one inlet, aconvergent/divergent means through which the liquid fuel and compressedgas pass, and a channel for supplying a hot oxidizing gaseous fluid tothe furnace,-the convergent/divergent means sealingly opening out intothe interiorol said channel 'for hot oxidizing gaseous fluid: theimprovement being a series of 'seco ndary chambers comprising at least afirst secondary chamber and a last secondary chamber, said firstsecondary chamber, communicating with said first chamber through anorifice; further injection inlets through which said compressed gaschannel opens into said secondary chambers,

said injection inlet into said first chamber being orientated such thatthe compressed gas injected therein mixes and atomizes the fuel suppliedinto said first chamber; said further injection inlets being orientatedsuch that the compressed gas injected into each secondary chamber meetsthe fuel and com,- pressed gas mixture issuing from the previoussecondary chamber in the series, whereby the atomization of the fuel iswhich is arranged in the interior of said channel for the hot oxidizinggaseous fluid.

13. The method as claimed in claim 1 comprising the further step ofexpanding said liquid fuel as it enters said first chamber by reducingthe pressure on the liquid fuel.

augmented; said convergent/divergent means being arranged adjacent tothe lastsecondary chamber in the series such that the fueland'compressed gas mixture can only leave said last l4. The method asclaimed in claim 5 wherein said inlets in the first and secondarychambers for compressed gas are tangential to the chamber

1. In a method for injecting fuel into a shaft furnace, comprisingintroducing a jet of liquid fuel into a first chamber, atomizing thefuel by means of a jet of compressed gas wherein the gas mixes with theatomized fuel, causing the mixture to converge and then diverge, thensubjecting the mixture to the action of a hot oxidizing gaseous fluid,and introducing the mixture of fuel gas and oxidizing fluid into theshaft furnace: the improvement comprising the steps of passing mixtureof fuel and compressed gas from said first chamber immediately throughat least one secondary chamber; introducing at least one further jet ofcompressed gas into said secondary chamber to augment the atomization ofthe fuel; and after causing the mixture to converge and then diverge,introducing the hot oxidizing gaseous fluid into the mixture in such aproportion that substantially all the fuel present in said mixture offuel and compressed gas is burned before being introduced along withsaid oxidizing fluid into the furnace.
 2. The method as claimed in claim1, comprising the further step of preheating at least one of said jetsof compressed gas before being introduced into a chamber.
 3. The methodas claimed in claim 2, in which said preheating is performed by said hotoxidizing gaseous fluid.
 4. The method as claimed in claim 1, in whichthe jet of compressed gas introduced into the last chamber through whichthe fuel and compressed gas mixture passes is substantially richer inoxygen than the jet of compressed gas in the prior chamber.
 5. In aninjector for the injection of liquid fuel into a shaft furnace,comprising a first chamber, a fuel line for supplying liquid fuel tosaid first chamber through at least one orifice, at least one inlet intosaid first chamber, a channel for injecting a compressed gas into saidfirst chamber through said inlet, a convergent/divergent means throughwhich the liquid fuel and compressed gas pass, and a channel forsupplying a hot oxidizing gaseous fluid to the furnace, theconvergent/divergent means sealingly opening out into the interior ofsaid channel for hot oxidizing gaseous fluid: the improvement being atleast one secondary chamber having an orifice, the secondary chambercommunicating with said first chamber through the orifice; at least oneinjection inlet through which said channel for the compressed gas opensinto said secondary chamber; said inlet in said first chamber beingorientated such that the compressed gas injected therein mixes with andatomizes the fuel supplied into said first chamber; said inlet in saidsecondary chamber being orientated such that the compressed gas meetsthe fuel and compressed gas mixture issuing from said first chamber andaugments the atomization of the fuel; said convergent/divergent meansbeing positioned adjacent said secondary chamber so that the fuel andcompressed gas mixture can only leave said secondary chamber by passingthrough the said means.
 6. The injector as claimed in claim 5, furthercomprising a frustoconical nozzle arranged convergently at the outlet ofsaid convergent/divergent means so as to leave a space between saidmeans and the nozzle, said nozzle being displaceable substantially alongthe axis of the injector.
 7. The injector as claimed in claim 5, furthercomprising means for supplying a gas rich in oxygen to the secondarychamber immediately before said convergent/divergent means.
 8. Theinjector as claimed in claim 5, wherein said fuel line is arranged inthe interior of said compressed gas channel, which channel is arrangedin the interior of said channel for the hot oxidizing gaseous fluid. 9.In an injector for the injection of liquid fuel into a shaft furnace,comprising a first chamber, a fuel line for supplying liquid fuel tosaid first chamber through at least one orifice, at least one inlet intosaid first chamber, a channel for injecting a compressed gas into saidfirst chamber through the said at least one inlet, aconvergent/divergent means through which the liquid fuel and compressedgas pass, and a channel for supplying a hot oxidizing gaseous fluid tothe furnace, the convergent/divergent means sealingly opening out intothe interior of said channel for hot oxidizing gaseous fluid: theimprovement being a series of secondary chambers comprising at least afirst secondary chamber and a last secondary chamber, said firstsecondary chamber communicating with said first chamber through anorifice; further injection inlets through which said compressed gaschannel opens into said secondary chambers, said injection inlet intosaid first chamber being orientated such that the compressed gasinjected therein mixes and atomizes the fuel supplied into said firstchamber; said further injection inlets being orientated such that thecompressed gas injected into each secondary chamber meets the fuel andcompressed gas mixture issuing from the previous secondary chamber inthe series, whereby the atomization of the fuel is augmented; saidconvergent/divergent means being arranged adjacent to the last secondarychamber in the series such that the fuel and compressed gas mixture canonly leave said last secondary chamber by passing through said means.10. The injector as claimed in claim 9, further comprising afrustoconical nozzle arranged convergently at the outlet of saidconvergent/divergent means so as to leave a space between said means andthe nozzle, said nozzle being displaceable substantially along the axisof the injector.
 11. The injector as claimed in claim 9, furthercomprising means for supplying a gas rich in oxygen to said lastsecondary chamber.
 12. The injector as claimed in claim 9, wherein saidfuel line is arranged in the interior of said compressed gas channelwhich is arranged in the interior of said channel for the hot oxidizinggaseous fluid.
 13. The method as claimed in claim 1 comprising thefurther step of expanding said liquid fuel as it enters said firstchamber by reducing the pressure on the liquid fuel.
 14. The mEthod asclaimed in claim 5 wherein said inlets in the first and secondarychambers for compressed gas are tangential to the chamber.